1. Field of the Invention
The present invention relates to an engine having a valve stopping mechanism capable of stopping operation of intake/exhaust valves for opening/closing a communication part between an engine cylinder chamber and an intake or exhaust path.
2. Description of Background Art
An engine is known having a valve stopping mechanism for stopping the operation of a part or all of intake/exhaust valves in a state where a valve drive cam rotates in accordance with an operating state of the engine.
As such a valve stopping mechanism, there is a configuration disclosed in JP-A No. H10-184327 wherein the valve stopping mechanism includes a lifter 11a which is reciprocated in a valve opening/closing direction by a valve drive cam 7, a lifter spring 24 for energizing the lifter 11a so that the lifter 11a abuts on the valve drive cam 7, and a plunger 23 sliding in a cylinder hole 21a formed extending at the right angle with the opening/closing direction in the lifter. In the plunger 23, a through hole 23b in which a valve shaft 5a of an exhaust valve 5 can be inserted and a power transmission face 23g on which the tip of the valve shaft 5a abuts are formed.
In the valve stopping mechanism, when the lifter 11a is reciprocated by the valve drive cam 7 in a state where the plunger 23 energized by the plunger spring 25 is moved to a stop position, the valve shaft 5a is inserted in a through hole 23a, and the exhaust valve 5 is held closed irrespective of the reciprocating movement of the lifter 11a, thereby obtaining a cylinder stop state. On the other hand, when the plunger 23 receives hydraulic fluid pressure on the side opposite to the plunger spring 25, the plunger 23 moves to the operating position against energization of the plunger spring 25. In this state, when the lifter 11a is reciprocated by the valve drive cam 7, the valve shaft 5a abuts on the power transmission face 23g and is reciprocated together with the lifter 11a, and the exhaust valve 5 is opened/closed, thereby obtaining a cylinder operating state.
In such a related valve stopping mechanism, the plunger 23 moves to the stop position by being energized by the plunger spring 25 and moves to the operating position by receiving hydraulic fluid from the opposite side. With this configuration, on start of an engine or the like, it takes time for the hydraulic fluid to become larger than the energizing force of the plunger spring. During the time, the valve is not opened/closed, and the cylinder stop state is obtained. Consequently, there is a problem such that it is difficult to obtain a sufficiently large engine output. To be concrete, for example, in the case of driving a hydraulic pump by an engine and generating the hydraulic fluid from a discharge of the hydraulic pump, when the engine is operated at very low speed on start of the engine or the like, it takes time for the hydraulic fluid to become large. During the time, the cylinder stop state is obtained. There is a problem such that it is difficult to increase an engine output.
To improve the steering feel for the driver, it is also requested to promptly switch from a valve stop state to a valve operating state by hydraulic control in response to a request for increasing an engine output of the driver, that is, to promptly switch from a cylinder stop state (state where the valve stops and the cylinder does not operate) to a cylinder operating state (state where the valve is opened/closed and the cylinder operates).